Craniofacial and especially orbital wall and floor defects may result from trauma, cancer, resection, or congenital defects. Such defects are typically treated surgically using bone grafts or synthetic implants. Congenital defects or fractures of the complex and relatively thin bone structures surrounding and supporting the human eye present difficult internal bone repair and fixation problems. In instances when the eye is subject to trauma, the margin or rim of the orbit may diffuse the force of the impact. However, compression of the orbital contents sometimes may occur and fracture the relatively fragile orbit floor and/or the lateral and medial orbital walls. Also injury at the lateral orbital rim may produce a fracture within the orbit. When the orbit is fractured standard bone-grafting techniques for orbital reconstruction may not result in predictable eye function and positioning. Often the support of the globe is deficient as a result of under correction of the defect, over correction, or inadequate reconstruction of the orbital volume. Further, the bone graph may be subject to resorption that may result in result in a less than optimal support. The accurate anatomical reconstruction of the bony orbit is essential to maintain normal function and appearance of the eye following orbital fractures. Because most of the bone of the internal orbit surfaces is thin, it is difficult to adequately stabilize the fractured bone fragments without the use of autogenous or alloplastic materials.
Damage to other craniofacial bones and the cranium may also occur from many of the above-listed sources, perhaps trauma and congenital defects being the most common. There are distinct needs to provide implants that can reconstruct these bones to restore and maintain normal function and appearance.
Autologous bone grafts have been considered an optimal treatment method for orbital floor and wall reconstruction, as well as other craniofacial and cranial defects. However, this material is sometimes difficult to obtain and difficult to shape the bone graft material to properly fit within the orbit or other area to be reconstructed. For example, there are problems relating to the tissue donor site morbidity. As discussed above, autogenous bone grafts have frequently been used by craniomaxillofacial surgeons for the reconstruction of the internal orbit. Bone may be harvested from the calvarium and other autogenous materials including iliac bone, split rib bone. Cartilage has also been used as a bone graft material. However, autogenous bones sometimes result in an unacceptable amount of resorption.
Accordingly, it is desirable to provide an improved implant for use in repairing and reconstructing craniofacial and cranial bones, as well as other non-weight bearing bones that may be damaged by trauma or other causes. A variety of alloplastic materials have been used for orbital reconstruction and craniofacial applications including, silicone rubber, Teflon, Supramid, tantalum mesh, Vitallium mesh, titanium mesh, polyethylene, and methyl methacrylate Perforated biocompatible metallic strips and metallic panels may be used for rigid internal fixation of fractures in trauma surgery and as a plate material for bone immobilization and stabilization. Metal implants can be used for bone graft support material in reconstructive surgery.
Synthetic implant materials have the advantage of no donor site morbidity, ease of use, relative low cost and ready availability. While there are advantages of synthetic implants, some characteristics may be regarded as disadvantages. Silicone rubber has a smooth surface, but does not allow fibrovascular ingrowth into the implant. Further, although it is flexible, it does not readily conform to the profile of the region where it is required or maintain a new shape when shaped to fit a particular location. For example, in connection with the reconstruction of the orbit, a silicone rubber implant is not an attractive option because upon shaping it to the desired profile, it will tend to be biased back to its original shape. While a silicone rubber implant does not maintain its shape, in a case where the soft tissues of the orbit have been traumatized, an implant with a smooth superior surface is desirable to prevent attachment of the tissues to the implant upon healing. Attachment of these tissues to the wall of the implant may result in restriction of movement of the eye, causing diplopia, dizziness, and headaches, as well as a cosmetic anomaly on upgaze, downgaze or lateral gaze.
Implants having a porous structure with predetermined pore sizes allow for fibrovascular ingrowth. In some circumstances, fibrovascular ingrowth is desirable because it integrates the implant within the tissues, and reduces the possibility that that the synthetic material will be rejected. Further, fibrovascular ingrowth on the inferior or sinus side of the implant allows for mucosalization of the implant surface, and since the opposite side of the implant may be a barrier, the sinus is effectively isolated from the soft tissues of the orbit. Similar issues arise in connection with the repair of other craniofacial bones. This arrangement is considered desirable because it increases the ability of the implant to ward off infection and minimizes the chance of a sinus infection from entering through the orbit. Fibrovascular ingrowth is also thought to minimize the chance of implant migration or displacement. However, although use of a material that is flexible and thin (appropriate for orbital floor and wall reconstruction) can be bent to an appropriate shape, the material tends to return to its original shape. Further, using a material that does not have a smooth superior surface, may result in restriction of the orbital tissues due to fibrous ingrowth when used for orbital reconstruction.
Pure titanium is the material of choice in craniofacial reconstructive surgery, especially when the implant is intended to be permanent. As an implant material, pure titanium is preferred because its low density and elastic modules are less than some of the stainless steel or cobalt-chromium alloys that have been used as implant materials. Titanium is corrosion resistant and, when provided in thin sheets, is pliable. Titanium implants many be cut and shaped to the appropriate configuration at the time of surgery. Titanium mesh is easily moldable in situ and easily fixed to bone, but does not have smooth surfaces, nor does it allow for fibrovascular ingrowth. An easily molded material is desirable for use in connection with embodiments of the present invention so that the surgeon can create the correct shape to properly reconstruct the orbital walls or orbital floor. Titanium mesh can be molded to the desired shape by hand and it will retain the shape due to the malleability and strength of the titanium material.
While there are a number of options for an implant material for orbital and other craniofacial reconstruction, there remains a need for a material that is easily moldable by hand and will retain its shape after molding, has a options for surface smoothness or porosity, and is made from highly biocompatible materials. Preferably it is desirable to provide an implant that can be trimmed and bent to shape to fit the shape of the orbital wall or orbital floor reconstruction, and placed in the orbit with the smooth surface on the inside, against the periosteum and soft tissues and with the porous side directed toward the sinus region. Further, it would be desirable to provide a material that can be fixed to the orbital bones with surgical screws or to the surrounding tissues with sutures.